Advances in window technology have reduced energy consumption by affecting and improving heating, cooling, and lighting. Various types of glass coatings have been developed for these purposes. Examples of glass coatings for reduced energy consumption include solar control coatings that reduce glare or overheating from the sun, and low-emissivity (“low-E”) coatings which reduce radiative heat gain or loss often accounting for significant heat transfer through a window.
Low-E coatings generally have a high reflectance in the thermal infrared (IR) and may or may not have high transmittance in the visible spectrum. Thus, they are low-emissive of thermal infrared. Some such coatings may admit solar near IR (NIR) to help heat a building, such as in a cold climate. Some such coatings may reflect the NIR back, such as in a warm climate. The low-emissivity optical properties are generally obtained by application of a material with certain intrinsic properties or alternatively, multiple materials may be combined to achieve the particular desired performance. Thin films of metals have been used to provide low emissivity coatings. Thin films forming infrared-reflection film are generally a conductive metal such as silver, gold or copper.
Coatings including such metals can be made highly transparent to visible radiation or light, while remaining reflective in the infrared. Such infrared-reflective coatings often include infrared-reflection materials and transparent dielectric materials. The infrared-reflection materials reduce the transmission of heat through the coating. The dielectric materials allow transmission of IR and visible light and control other properties and characteristics of the coating, such as color and durability. However, solar heat gain via windows having highly reflective coatings remains a concern to builders and tenants desiring energy efficiency.
Accordingly, there is a need in the industry for a coating for a visible light transmissive substrate that provides improved solar heat gain coefficients over currently available coatings and coated substrates while also providing the visible light transmission benefits of metal coatings.